Hi,
If videotestsrc can achieve 60fps, ideally v4l2src should achieve the same. A bit strange the result is different. For GRAY8 input, Raw2NvBuffer() is required and after executing $ sudo nvpmodel -m 0, $ sudo jetson_clocks, it runs in optimal throughput. There may not be room for improvement.
One more try is to run VIC at max clock. Please refer to:
Nvvideoconvert issue, nvvideoconvert in DS4 is better than Ds5? - #3 by DaneLLL